There has been increasing interest in converting cellulosic biomass to fuels or other chemicals. There are many biomass conversion processes, including acid hydrolysis, enzymatic hydrolysis, and gasification. One biomass conversion process gaining traction is hydrothermal treatment, which typically includes a first step of contacting a biomass with hot compressed water, with or without an acid catalyst. This step typically enables the extraction and hydrolysis of hemicellulosic sugars and, in under certain conditions, the hydrolysis of cellulose to sugars. Depending on the time and temperature of the treatment, and the catalyst loading (if used), the hemicellulosic sugars are either partially or completely extracted. Subsequent steps may include further treatment of the remaining unconverted biomass (e.g., cellulose), as well as transformation of the extracted sugars from the first step into ethanol or other useful chemicals.
In the first step of this process, hemicellulose typically is converted to monomeric and oligomeric sugars, such as xylose, xylo-oligosaccharides, rhamnose, arabinose, galactose, and mannose. The ratio of oligomers-to-monomers varies depending on the severity of the reaction (e.g., the time, pressure and temperature history, and the catalyst amount, if used). The reaction also generates by-products and/or degradation products, such as acetic acid, furfural, hydroxylmethyl furfural (HMF), and organic acids, such as formic acid and levulinic acid.
In the pulp and paper industry, biomass processing methods are designed to extract the hemicellulose and most of the lignin from the lignocellulosic biomass by the addition of chemicals (e.g., using the Kraft process or sulfite process), leaving most of the cellulose behind. Typically no measures are taken to maximize the yield of sugars extracted (e.g., xylose and/or xylo-oligosaccharides), because the focus of these technologies is on producing cellulose for making paper or paper products. Moreover, many processes employ chemicals to facilitate the extraction or recovery of cellulose, but these processes are more expensive than those that do not employ chemicals. Even in situations where it may be desirable to maximize the extraction yield of hemicellulosic sugars, such methods are only optimized for one biomass feedstock.
In order to sustain large production rates of sugars derived from biomass and the subsequent ethanol production, it may be necessary to mix different biomasses for processing. Utilizing mixtures of different biomasses for processing presents a significant challenge for conversion to sugars, especially for hemicelluloses extraction. Different biomasses hydrolyze at different rates, and the hydrolysis rate may depend on a variety of factors. If mixtures of biomass are hydrolyzed without accounting for the large variability in hydrolysis rates of the component biomasses in the mixture, the sugar yields will be lower than the potential maximum yields, and the production of degradation products typically will be increased.
Thus, there is an ongoing need for methods for maximizing sugar yields from mixtures of biomass. The methods of the present invention are directed toward these, as well as other, important ends.
It will be appreciated that this background description has been created by the inventors to aid the reader and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims and not by the ability of any disclosed feature to solve any specific problem noted herein.